¤ West Warwick, Rhode Island 02893

SIZING THETHERM-X-TROL®

POTABLE WATEREXPANSION TANK

Part #: 9017-112 (1/04)

Sizing the Therm-X-Trol® PotableWater Expansion TankAs water is heated, thermal expansion takes place. This small

volume of water can cause rapid increases in system pressure

if a backflow preventer or other one-way device is installed with-

out the proper thermal expansion tank. Examples of one-way

devices include:

• Backflow Preventers (BFP’s)

• Check Valves

• Pressure Reducing Valves (PRV’s)

ASME Therm-X-Trol® expansion tanks incorporate a

polypropylene liner and non-ferrous materials suitable for use

with domestic potable water systems. In the following pages,

you’ll find helpful information to assist you in the sizing and

general installation requirements of Therm-X-Trol® tanks.

Here’s how the ASME Therm-X-Trol® works:As can be seen, the ASME Therm-X-Trol® tank assumes animportant role in reducing water heater damage. Next, we’llbegin the process of sizing a thermal expansion tank.

ASME CodeThe ASME boiler pressure vessel code is quite explicit on

exemptions from ASME requirements. ASME Section VIII,

Division 1 (U-1)(c)(2) states: “Based on the committee’s

consideration, the following classes of vessels are included in

the scope of this Division: a vessel for containing water under

pressure, including those containing air the compression of

which serves only as a cusion, when one of the following

limitations are exceeded:

a) a design pressure of 300 psi (2070 kPa)

b) a design temperature of 210˚F (99˚C)

AMTROL Therm-X-Trol models ST-5 through ST-210V have a

maximum working pressure of 150 psi, and a maximum design

temperature of 200˚F. These models are, therefore, exempt.

Local code authorities having jurisdiction may follow this criteria,

utilize guidelines with additional volumetric constraints, or develop

requirements independent of these ASME suggested criteria. It is

the responsibility of the designer to meet the requirements of the

authority having jurisdiction. For interpretation of local code

guidelines, contact the AMTROL technical representative in your

area.

Typical Engineering SpecificationFurnish and install as shown on plans a _________ gallon,

_________” diameter x ______” (high) pre-charged hydropneu-

matic steel expansion tank. The tank construction shall be in

accordance with Section VIII, Division 1 of the ASME Boiler and

Pressure Vessel Code, with all welds conforming to ASME

Section IX. The tank must be stamped with a maximum working

pressure of _______psi and a maximum working temperature of

________˚ F. All internal wetted parts must comply with FDA

regulations and approvals. An internal butyl/EPDM diaphragm or

butyl bladder will be used to isolate air charge from water.

Each tank shall be AMTROL Therm-X-Trol Model No.

ST-______-C.

ASME Water Heater On

Expanded Water enters the ASME Therm-X-Trol®

ASME Therm-X-Trol®

Backflow Preventer

Expanded Water

MC# 10007

®

*Based on initial temperature of 40˚ F.

For conditions not shown in table, use equation:

The procedure for sizing the Therm-X-Trol for any applicationdepends on four(4) vital pieces of information:

1. ASME or non-ASME requirement.2. Calculated thermally expanded water volume.3. Minimum water pressure experienced at the tank location.4. Maximum water pressure allowable at the tank location.

The tank required for any application can be sized with the following equation:

Tv = Design Pressure Factor x expanded waterWhere: Tv is the total Therm-X-Trol volume required

in gallons.

Critical Sizing AMTROL Therm-X-Trol1. Total Water Heater Volume (Gallons) 1.2. Water Expansion Factor (Table 1) 2.3. Calculate Expanded Water (Gallons) 3.

(Line 1 x Line 2)4. Design Pressure Factor (Table 2) 4.5. Therm-X-Trol Volume Required (Gallons) 5.

(Line 3 x Line 4)6. Select Therm-X-Trol Model 6.

Example: A 240 gallon water heater with a 150˚F aquastat set-ting is installed with a 125 psi maximum pressure requirement.For static supply line pressure of 60 psi, what Therm-X-Trolmodel is required for critical protection?

Critical Sizing AMTROL Therm-X-Trol: Example1. Total Water Heater Volume (Gallons) 2402. Water Expansion Factor (Table 1) 0.01793. Calculate Expanded Water (Gallons) 4.3

(Line 1 x Line 2) = (240 x .0179)4. Design Pressure Factor (Table 2) 2.15. Therm-X-Trol Volume Required (Gallons) 9.0

(Line 3 x Line 4) = (4.3 x 2.1)6. Select Therm-X-Trol Model ST-25V

or ST30V-C

Notes:The THER-X-TROL air pressure should be equal to static linepressure.When sizing a THERM-X-TROL, the unit must meet the calcu-lated expanded water (step 3 in example) and total tank volume(step 5 in example).

Basic Tank Installation ConsiderationsNow that the proper expansion tank has been selected, it istime to install the unit.

Tank PrechargeThe pre-charge equalization of the tank and incoming supplypressure is a critical step and if done improperly can contributeto premature tank failure. As Boyle’s law showed us, air pressuredetermines the ability to cushion expanded water. As such, it isimportant to properly charge the Therm-X-Trol before installation.Standard Therm-X-Trol tanks are shipped at 40 psi. How doesthe air charge affect the tank’s operation? Let’s take a look at our70 psi incoming pressure if the tank is left at 40 psi:

Note how the 70 psi incomingpressure pushes against thediaphragm and takes up valu-able space before the waterhas even begun to heat andexpand. Because of this, it isnecessary to match theprecharge to the incoming sup-ply pressure before installation.See below:

Tank LocationPlacement of an expansion tank isimportant for two reasons.1. Location affects the tank’s

ability to absorb water2. Improper placement can tem-

porarily affect water deliverytemperature

Let’s look at a typical hot watersystem:

-2-

ASMEWater Heater

(Storage Tank)

CWS

Relief Valve

HWS

Backflow Preventer,Check Valve orPressure ReducingValve

In-Line Installation

ASMETherm-X-Trol

70 PSI

40 PSI

70 PSI

70 PSI

Max. Allow. Pressure + 14.7Max. Allow. Pressure - Line Pressure

DPF=

Operating (Design) Expansion Factor*Temperature of (Percentage of Water

Water Heater (Tank) Volume Increase)100˚ F .0062 0.6%120˚ F .0100 1.0%130˚ F .0124 1.2%140˚ F .0150 1.5%150˚ F .0179 1.8%160˚ F .0209 2.0%170˚ F .0242 2.4%180˚ F .0276 2.8%

Maximum Line DesignAllowable Pressure PressurePressure psi Factor (DPF)

40 1.950 2.360 2.970 3.880 5.740 1.650 1.960 2.170 2.580 3.140 1.550 1.660 1.870 2.180 2.4

100

125

150

Table 1. Expansion Factor

Table 2. Design Pressure Factor: DPF

Note the backflow preventer separating the cold water supplyand water heater. The backflow preventer will not allow waterto flow back to the supply. It is therefore necessary to installthe Therm-X-Trol® on the cold water supply after the backflowpreventer.

Now that we have established the proper side of the system forinstallation of the Therm-X-Trol®, let’s look at the Therm-X-Trol®’s relation to the position of the water heater.

In the diagram below, the Therm-X-Trol® has been properlyplaced on the cold supply entering the water heater. As thermalexpansion takes place, a small volume of water from the heaterflows into the tank. Upon water use, the tank will release thisabsorbed water allowing it to flow into the heater.

Let’s explore the effect of placing the Therm-X-Trol® on the hotwater outlet. As thermal expansion takes place, heated waterflows from the water heater outlet into the expansion tank. Aswater sits in the tank, it begins to cool. As previously explained,water is expelled from the tank during a demand. Since thiswater has cooled, hot water will not be immediately available atthe fixtures.

Mounting Position

One benefit inherent in the Therm-X-Trol® is the ability tomount the tank in any position. Due to the use of a heavybutyl/EPDMdiaphragm or butyl bladder, the Therm-X-Trol® canbe mounted in an arrangement that best suits the installationspace.

This Technical Bulletin is intended to provide general informationfor use in assessing the propriety of the Therm-X-Trol® for yourresidential hot water application. It is not an installation and/oroperation manual. The detailed steps for proper installation andoperation of the Therm-X-Trol® are published in the AMTROLProduct Installation Manual for this product. Proper installationand operation of the Therm-X-Trol® requires, among other things,consideration of local building ordinances and plumbing codes,appropriate situation and configuration of the unit, and compli-ance with all pre-installation requirements and post-installationoperation and maintenance procedures.

-3-

ASMEWater Heater

(Storage Tank)

CWSCWS

HWS

Floor Standing Installation

ASME Therm-X-Trol

Incorrect

ASMEWater Heater

(Storage Tank)

CWS

Relief Valve

HWS

Backflow Preventer,Check Valve orPressure ReducingValve

ASMETHERM-X-TROL

ASMEWater Heater

(Storage Tank)

CWS

Relief Valve

HWS

Backflow Preventer,Check Valve orPressure ReducingValve

Correct

ASMETHERM-X-TROL

Correct

Expanded Water enters the Therm-X-Trol®

ASMEWater Heater

ASMETHERM-X-TROL

Incorrect

To Fixtures

ASMEWater Heater

ASMETHERM-X-TROL

THERM-X-TROL® Replaceable Bladder Design ASME TanksModel Max. Working Total Volume Recommended Diameter Height System Ship Weight

No. Pressure (PSIG) (Gals.) Acceptance Volume (A) (B) Connection (lbs)ST-447-C 125/150 53.0 34.45 24" 45 1/4" 2" NPT 263ST-448-C 125/150 80.0 52.00 24" 59 1/8" 2" NPT 308ST-449-C 125/150 106.0 68.90 24" 73 1/8" 2" NPT 353ST-450-C 125/150 132.0 85.80 24" 86 5/8" 2" NPT 391ST-451-C 125/150 158.0 102.70 30" 73 1/4" 2" NPT 508ST-452-C 125/150 211.0 137.15 30" 91" 2" NPT 760ST-453-C 125/150 264.0 171.60 36" 85 5/8" 3" NPT 810ST-454-C 125/150 317.0 206.05 36" 98" 3" NPT 914ST-455-C 125/150 370.0 240.50 36" 110 3/8" 3" NPT 1,018ST-456-C 125/150 422.0 274.30 48" 81 7/8" 3" NPT 1,655ST-457-C 125/150 528.0 343.20 48" 97 1/4" 3" NPT 1,925

Maximum Allowable Working Temperature: ST-5-C through ST-210V-C: 200°F; ST-447-C through ST-457-C: 240°FStandard Factory Precharge: 55 PSIG. All Models listed by NSF 61 (excluding ST-447-C through ST-457-C). ST-447-C through ST-457-C are replaceable bladder design.

West Warwick, Rhode Island 02893

A

B

A

B

A

B

A

B

ST-5-C,ST-12-C

ST-20V-C to ST-70V-C

ST-80V-C to ST-210V-C

ST-447-C to ST-457-C

A

B

A

B

ST-5, ST-12

ST-25V through ST-210V

THERM-X-TROL Non-ASME Specifications Model Total Volume Maximum Diameter Height System Ship Weight

No. (Gals.) Acceptance (Gals.) (A) (B) Connection (lbs)ST-5 2.0 .9 8" 12 5/8" 3/4" NPT 5ST-12 4.4 3.2 11" 15" 3/4" NPT 9

ST-25V 10.3 10.3 15 3/8" 19 1/4" 1" NPT 23ST-30V 14.0 11.3 15 3/8" 23 7/8" 1" NPT 25ST-42V 20.0 11.3 15 3/8" 31 5/8" 1" NPT 33ST-60V 34.0 34 22" 29 5/8" 1 1/4" NPT 61ST-80V 44.0 34 22" 36" 1 1/4" NPT 69ST-180V 62.0 34 22" 46 3/4" 1 1/4" NPT 92ST-210V 86.0 46 26" 47 1/4" 1 1/4" NPT 123

THERM-X-TROL Replaceable Bladder DesignModel Total Volume Diameter Height System Ship Weight

No. (Gals.) (A) (B) Connection (lbs)ST-451 158.0 73 1/4" 30" 2" NPT 508ST-452 211.0 91" 30" 2" NPT 760ST-453 264.0 85 5/8" 36" 3" NPT 810ST-454 317.0 98" 36" 3" NPT 914ST-455 370.0 110 3/8" 36" 3" NPT 1,018ST-456 422.0 81 7/8" 48" 3" NPT 1,655ST-457 528.0 97 1/4" 48" 3" NPT 1,925

Maximum Working Pressure: 150 PSI. All Models listed by NSF 61 (excluding ST-451 – ST-457); Maximum Allowable WorkingTemperature: ST-5 through ST-210V: 200°F; ST-451 through ST-457: 240°F; Standard Factory Precharge: 40 PSIG (ST-5 – ST-210V); 55 PSIG (ST-451 – ST-457)

The AMTROL logo and THERM-X-TROL are registered trademarks of AMTROL, Inc. In the interest of continuous development, AMTROL Inc. and its subsidiaries reserve the right to alter designs and specifications without prior notice.

THERM-X-TROL® ASME SpecificationsModel Max. Working Total Volume Maximum Diameter Height System Ship Weight

No. Pressure (PSIG) (Gals.) Acceptance (Gals.) (A) (B) Connection (lbs)ST-5-C 150 2.1 .9 10" 10 3/8" 3/4" NPT 21ST-12-C 150 6.4 3.2 12" 15 5/8" 3/4" NPT 26

ST-20V-C 150 8.0 3.2 12" 19 1/2" 3/4" NPT 41ST-30V-C 150 14.0 10.5 16 1/4" 19 1/8" 3/4" NPT 84ST-42V-C 150 17.5 11.3 16 1/4" 24 1/4" 3/4" NPT 90ST-60V-C 150 25.0 11.3 16 1/4" 34" 3/4" NPT 96ST-70V-C 150 34.0 11.3 16 1/4" 45 3/4" 3/4" NPT 123ST-80V-C 150 53.0 34 24" 40 1/2" 1 1/4" NPT 229ST-120V-C 150 66.0 34 24" 47 3/4" 1 1/4" NPT 258ST-180V-C 150 77.0 34 24" 52 5/8" 1 1/4" NPT 288ST-210V-C 150 90.0 34 24" 60" 1 1/4" NPT 318